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Organic Electroluminescent Element And Compounds For Use In The Element - Patent 8147987

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Organic Electroluminescent Element And Compounds For Use In The Element - Patent 8147987 Powered By Docstoc
					
				
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Description: 1. Field of the Invention The present invention relates to a light-emitting element which can convert electric energy to light to emit light, in particular, to an organic electroluminescent element and novel compounds to be used therein. 2. Description of the Related Art An organic electroluminescent (EL) element has attracted attention since it can provide luminescence with a high luminance at a low voltage. As an important characteristic value of this organic electroluminescent element, there exists externalquantum efficiency. The external quantum efficiency is calculated by the formula of "external quantum efficiency .phi.=a number of photons emitted from an element/a number of electrons injected into the element". An element having higher external quantum efficiency can be said to be advantageous in view of electric power consumption. The external quantum efficiency of an organic electroluminescent element is determined according to the formula of "external quantum efficiency .phi.=internal quantum efficiency.times.light extraction efficiency". In an organic EL elementutilizing fluorescent luminescence from an organic compound, the limit value of internal quantum efficiency is 25%, and light extraction efficiency is about 20%, and hence the limit value of external quantum efficiency is believed to be about 5%. As a method of improving external quantum efficiency of an element by improving the internal quantum efficiency of an organic electroluminescent element, an element (a triplet light-emitting element) using a triplet light-emitting material(phosphorescent luminescence material) has been reported (WO00/070655). In comparison with conventional elements utilizing fluorescent luminescence (singlet light-emitting element), this element can improve the external quantum efficiency, and themaximum value of the external quantum efficiency of an element using Ir(ppy).sub.2 which is a green-color phosphorescent material has amounted to 8% (external quantum effi